Rotor blade tip planform

Abstract

An aerofoil has a main portion of aerofoil cross section, an inner spanwise root end where the aerofoil is in use secured to a supporting structure, and at an outermost spanwise end outboard of the main portion, beyond a tip station, a tip region which includes a tip edge. The planform configuration of the tip edge lies on a first Bezier curve constructed from at least four control points, P 1 , P 2 , P 3 and P 4 , each lying on the periphery of a polygon which bounds the tip region. Control point P 1 is located on a leading edge of the aerofoil. Control point P 2 is located on the second side of the polygon. Control point P 3 is located on the third side of the polygon, and control point P 4 is located at the outermost tip edge point at a trailing edge of the aerofoil.

The invention claimed is: 
     
       1. An aerofoil having a main portion of aerofoil cross section, an inner spanwise root end where the aerofoil is in use secured to a supporting structure, and at an outermost spanwise end outboard of the main portion, beyond a tip station, a tip region, and the tip region including a tip edge,a planform configuration of the tip edge following a first Bezier curve constructed from at least four control points P 1 , P 2 , P 3  and P 4 , the control points P 1 , P 2 , P 3  and P 4  each following a periphery of a polygon which bounds the tip region, Bezier control point P 1  being located on a leading edge of the aerofoil at the tip station, which is at a spanwise position between 93.5% R and 95.9% R, where first and second sides of the polygon meet, the first side being at the tip station extending perpendicularly to a blade reference axis, which extends spanwise of the main portion of the aerofoil, and the second side being a tangent to the leading edge of the aerofoil at control point P 1 , which extends between control point P 1  to a position where the second side meets a third side of the boundary polygon at a position outwardly of the tip edge, the third side being parallel to the first side and extending between the position where the third side meets the second side, to where the third side and a fourth side meet, control point P 2  being located on the second side at a position between 30% and 80% along the second side from P 1 , control point P 3  being located on the third side at a position between 30% and 90% along the third side from where the second and third sides meet, and control point P 4  being located at an outermost tip edge point at a trailing edge of the aerofoil, where R is the effective aerofoil span. 
     
     
       2. An aerofoil according to  claim 1  wherein the Bezier curve on which the planform configuration of the tip edge of the tip region lies, is a cubic Bezier curve. 
     
     
       3. An aerofoil according to  claim 1  wherein the boundary polygon is one of a rectangle, a parallelogram or trapezium. 
     
     
       4. An aerofoil according to  claim 3  wherein the fourth side of the boundary polygon is a tangent to a trailing edge of the aerofoil where the first side meets the trailing edge, and the fourth side extending between where the first side meets the trailing edge and the fourth side meets the third side. 
     
     
       5. An aerofoil according to  claim 1  wherein the outermost tip edge point lies on the third side. 
     
     
       6. An aerofoil according to  claim 5  wherein the outermost tip edge point lies on the third side where the third side meets the fourth side. 
     
     
       7. An aerofoil according to  claim 5  wherein the outermost tip edge point lies on the third side between control point P 3  and where the third and fourth sides of the boundary polygon meet. 
     
     
       8. An aerofoil according to  claim 1  wherein the tip edge of the aerofoil has a rounded leading edge corner which extends to an edge part which extends substantially streamwise, so that the tip edge is of a swept back configuration from the control point P 1 . 
     
     
       9. An aerofoil according to  claim 1  wherein the planform configuration of the trailing edge of the aerofoil at the tip region lies on a second Bezier curve constructed from at least two further control points P 5 , and P 8 , control point P 5  being located where the first side of the boundary polygon meets the trailing edge, and control point P 8  being located at the outermost tip edge point. 
     
     
       10. An aerofoil according to  claim 9  wherein the second Bezier curve between the control points P 5  and P 8  is a straight line which extends generally parallel to the blade reference axis. 
     
     
       11. An aerofoil according to  claim 9  wherein the second Bezier curve is constructed from three control points P 5 , P 6  and P 8 , the control point P 6  being located at an intersection of first and second trailing edge control point reference lines, the first trailing edge control point reference line being a tangent to the trailing edge inboard of the tip station, at control point P 5 , the first trailing edge control point reference line extending at a sweep angle to the blade reference axis, and the second trailing edge control point reference line being a line which passes through control point P 8  at the outermost tip edge point and extends at an angle to the blade reference axis which is between zero and 1.5 times the sweep angle. 
     
     
       12. An aerofoil according to  claim 11  wherein the second trailing edge control point reference line extends at an angle to the blade reference axis which is between zero and the sweep angle. 
     
     
       13. An aerofoil according to  claim 11  wherein the sweep angle is between zero and 30°. 
     
     
       14. An aerofoil according to  claim 9  wherein the second Bezier curve is constructed from four control points P 5 , P 6 , P 7  and P 8 , the control point P 6  being located along a first trailing edge control point reference line which is a tangent to the trailing edge inboard of the tip station, at control point P 5 , the first trailing edge control point reference line extending at a sweep angle to the blade reference axis, and the control point P 7  is located along a second trailing edge control point reference line being a line which passes though point P 8  at the outermost tip edge point and extends at an angle to the blade reference axis which is between zero and 1.5 times the sweep angle. 
     
     
       15. An aerofoil according to  claim 14  wherein the control point P 6  is located along the first trailing edge control point reference line at a position between 10% and 33% of the spanwise extent of the tip region from control point P 5  but not spanwise outwardly of the intersection of the first and second trailing edge control point reference lines, and the control point P 7  is located along the second trailing edge control point reference line at a position between 66% and 90% of the spanwise extent of the tip region from control point P 5  but not spanwise inwardly of the intersection of the first and second trailing edge control point reference lines. 
     
     
       16. An aerofoil according to  claim 14  wherein the second Bezier curve on which the trailing edge of the aerofoil at the tip region lies, is a cubic Bezier curve. 
     
     
       17. An aerofoil according to  claim 1  wherein the tip region has anhedral. 
     
     
       18. An aerofoil according to  claim 17  wherein the aerofoil has a chordal plane which extends over the aerofoil between the leading edge and the trailing edge over the main portion of the aerofoil, and the anhedral follows a curve in a vertical plane which is perpendicular to the chordal plane, the curve being between pressure and suction surfaces of the aerofoil over the tip region, and the curve being a third Bezier curve constructed from at least three control points P 9 , P 10 , and P 12  in the vertical plane, and wherein control point P 9  is located spanwise of the aerofoil at the tip station, and on the chordal plane, control point P 12  is located at the outermost tip edge point, and control point P 10  being located at an intersection of first and second anhedral control point reference lines, the first anhedral control point reference line being coincident with the chordal plane, and the second anhedral control point reference line passing through control point P 12  and extending at a tip anhedral angle to the chordal plane, at between 4° and 30°. 
     
     
       19. An aerofoil according to  claim 17  wherein the aerofoil has a chordal plane which extends over the aerofoil between the leading edge and the trailing edge over the main portion of the aerofoil, and the anhedral follows a curve in a vertical plane which is perpendicular to the chordal plane, the curve being between pressure and suction surfaces of the aerofoil over the tip region, and the curve being a third Bezier curve constructed from at least four control points P 9 , P 10 , P 11  and P 12  in the vertical plane, and wherein control point P 9  is located spanwise of the aerofoil at the tip station, and on the chordal plane, control point P 12  is located at the outermost tip edge, and first intermediate control point P 10  being located along a first anhedral control point reference line which is coincident with the chordal plane, and second intermediate control point P 11  being located on a second anhedral control point reference line which passes through control point P 12  and extends at a tip anhedral angle to the chordal plane, at between 4° and 30°. 
     
     
       20. An aerofoil according to  claim 19  wherein the first intermediate control point P 10  is located along the first anhedral control point reference line at a position between 20% and 55% of the spanwise extent of the tip region from control point P 9 , but not spanwise outwardly of the intersection of the first and second anhedral control point reference lines, and the second intermediate control point P 11  is located along the second anhedral control point reference line at a position between 55% and 90% of the spanwise extent of the tip region from control point P 9  but not spanwise inwardly of the intersection of the first and second anhedral control point reference lines. 
     
     
       21. An aerofoil according to  claim 20  wherein the first intermediate control point P 10  is located along the first anhedral control point reference line at a position at about 33% of the spanwise extent of the tip region from control point P 9 , and the second intermediate control point P 11  is located along the second anhedral control point reference line at a position at about 66% of the spanwise extent of the tip region from control point P 9 . 
     
     
       22. An aerofoil according to  claim 19  wherein the second anhedral control point reference line which passes through control point P 12 , extends at a tip anhedral angle to the chordal plane, at between 4.4° and 25°. 
     
     
       23. An aerofoil according to  claim 1  in which the main portion of the aerofoil extends from the supporting structure spanwise for at least 75% of the overall aerofoil effective span. 
     
     
       24. A aerofoil according to  claim 1  wherein the blade reference axis extends spanwise of the main portion of the aerofoil mid the mean thickness of the main portion of the aerofoil, and at least the main portion of the aerofoil has a twist of between 0° and 16° therealong, about the blade reference axis. 
     
     
       25. An aerofoil according to  claim 1  wherein the aerofoil is secured at the root end to a rotating supporting structure. 
     
     
       26. An aerofoil according to  claim 1  wherein the aerofoil includes a tip panel located between the main portion of the aerofoil and the tip region, the tip panel extending outwardly spanwise from a tip panel station at between 85% R and 88% R to the tip station. 
     
     
       27. An aerofoil according to  claim 26  wherein the blade reference axis is located at 0.25C where C is the chord length of the main portion of the aerofoil, and wherein the tip panel has a leading edge which sweeps rearwardly from the tip panel station to the tip station, the leading edge of the aerofoil at the tip station being located at or rearwardly of where the blade reference axis intersects the leading edge. 
     
     
       28. An aerofoil according to  claim 26  wherein between the tip panel and the main portion of the aerofoil there is a blend region at which leading and trailing edges of the main portion blend with respective leading and trailing edges of the tip panel, the blend region extending outwardly spanwise from a blend region station at about 75% R to the tip panel station. 
     
     
       29. An aerofoil according to  claim 28  wherein at least portions of the leading edges of each of the blend region and the tip panel extend forwardly of the leading edge of the main portion of the aerofoil. 
     
     
       30. An aerofoil according to  claim 28  wherein at least portions of the leading edges of each of the blend region and tip panel lie on one or more Bezier curves constructed from control points. 
     
     
       31. A method of providing an aerofoil which includes a main portion of aerofoil cross section, an inner spanwise root end where the aerofoil is in use secured to a supporting structure, and at an outermost spanwise end outboard of the main portion, beyond a tip station, a tip region, and the tip region including a tip edge, a planform configuration of the tip edge following a first Bezier curve constructed from at least four control points P 1 , P 2 , P 3  and P 4 , the control points P 1 , P 2 , P 3  and P 4  each following a periphery of a polygon which bounds the tip region, Bezier control point P 1  being located on a leading edge of the aerofoil at the tip station, which is at a spanwise position between 93.5% R and 95.9% R, where first and second sides of the polygon meet, the first side being at the tip station extending perpendicularly to a reference axis which extends spanwise of the main portion of the aerofoil, and the second side being a tangent to the leading edge of the aerofoil at control point P 1 , which extends between control point P 1  to a position where the second side meets a third side of the boundary polygon at a position outwardly of the tip edge, the third side being parallel to the first side and extending between the position where the third side meets the second side, to where the third side and a fourth side meet, control point P 2  being located on the second side at a position between 30% and 80% along the second side from P 1 , control point P 3  being located on the third side at a position between 30% and 90% along the third side from P 2 , and control point P 4  being located at the outermost tip edge point at a trailing edge of the aerofoil, where R is the effective aerofoil span, the method including shaping the planform configuration of the tip edge to follow the first Bezier curve.